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NEC TG-16/TE/TurboDuo => TG/PCE Repair/Mod Discussion => Topic started by: Raulie on June 09, 2015, 07:07:15 AM

Title: No video/audio through Super CD-ROM² output
Post by: Raulie on June 09, 2015, 07:07:15 AM

Hi guys,

I bought a Super CD-ROM² with no sound, and when I tested it out there was no video/audio through Super CD-ROM² output.

If I connect the A/V cable to the Core Grafx, the games play perfectly, but obviously with no CD audio. I’ve replaced all the capacitors and there’s no difference.

The volume balance IC (M51131L) has only 0.77V as supply voltage.

I would be happy, if I could fix just the audio. For video, I can have the RGB mod.

Any ideas?

Regards,
Raulie

Title: Re: No video/audio through Super CD-ROM² output
Post by: pnauts on June 09, 2015, 10:32:19 AM

Here are the Values I measured once for a fixed one:

1: 8V (V supply)
2: 3.4V (input 1)
3: 3.1V (output 1)
4: 5.52V (Vréf)
5: 8V (Low pass filter)
6: not connected
7: gnd
8: 5V (volume control)
9: gnd
10: 2.8V (Balance control)
11: gnd
12: 5.52V (wire to 4)
13: 3.1V (output 2)
14: 3.4V (input 2)

It seems that you have to check the traces on your supply pin.

Title: Re: No video/audio through Super CD-ROM² output
Post by: Raulie on June 10, 2015, 01:42:23 AM

Thanks for your response pnauts!

There was a broken trace between C305 and R306. Now, I have video, but still no audio.

I've checked the values of every pin and now they're pretty similar to your values:

1 = 7.97V
2 = 2.96V
3 = 3.09V
4 = 5.58V
5 = 7.70V
6 = 0V
7 = 0V
8 = 4.92V
9 = 0V
10 = 2.72V
11 = 0V
12 = 5.58V
13 = 3.1V
14 = 2.95V

At least, now I know that the M51131L is fine.

Title: Re: No video/audio through Super CD-ROM² output
Post by: Raulie on June 10, 2015, 03:05:03 AM

I turned up the volume, and there's sound! Low crackling sound though.

I read that was your problem pnauts. So, I think I just need to clean the pcb. Let's see...

Title: Re: No video/audio through Super CD-ROM² output
Post by: pnauts on June 10, 2015, 03:20:37 AM

Check pin 4 on CN103 connector, the voltage should be as low as possible to 0V. According to the result, probably the 1000µF capacitor next to the heatsink leaked on a via located under this cap.

Title: Re: No video/audio through Super CD-ROM² output
Post by: Raulie on June 10, 2015, 11:12:46 AM

Hmm... Right now, it's 1.02V. I removed that cap, and it was pretty clean. I cleaned it again though.
It made no difference.

I'm going to verify all the traces related to that pin.

Thanks!

Title: Re: No video/audio through Super CD-ROM² output
Post by: pnauts on June 10, 2015, 12:29:13 PM

you should have twice less minimum at cold, and a decrease as soon as the time goes by.
Follow the trace from the via under the cap and clean it, there is perhaps another issue.

Title: Re: No video/audio through Super CD-ROM² output
Post by: Raulie on June 11, 2015, 05:48:13 AM

What a maze! I finally found where pin 4 is connected. It's connected to 2 diodes, which are connected to some transistors, near the 1000µF cap:

(http://pic.photobucket.com/bwe.png) (http://s140.photobucket.com/user/freakpunker/media/pin4_zpsyw4xksdk.jpg.html)

That's it for today... LOL!

Title: Re: No video/audio through Super CD-ROM² output
Post by: pnauts on June 11, 2015, 10:47:41 AM

I should have a complete scheme for this one, but I can't have a look before next week.

Title: Re: No video/audio through Super CD-ROM² output
Post by: Raulie on June 13, 2015, 08:29:54 AM

I got desperate, and I washed the pcb using a hose, a toothbrush, and Palmolive. Now, the sound is perfect!  :D

Title: Re: No video/audio through Super CD-ROM² output
Post by: thesteve on June 13, 2015, 04:25:09 PM

lol
dishwasher works too

Title: Re: No video/audio through Super CD-ROM² output
Post by: pnauts on June 14, 2015, 07:03:25 AM

I think it's better to use isopropylic (exact english name?) alcohol, but nevertheless it works.
I hope for you it'll keep this way.

Title: Re: No video/audio through Super CD-ROM² output
Post by: thesteve on June 14, 2015, 12:01:04 PM

sadly alcohol doesnt work as well as high temp detergent

Title: Re: No video/audio through Super CD-ROM² output
Post by: pnauts on June 14, 2015, 09:17:51 PM

mmm... I would worry about cleaning old parts this way for long terms issue (porosity ? humidity ?) perhaps for no reason

Title: Re: No video/audio through Super CD-ROM² output
Post by: thesteve on June 15, 2015, 09:08:03 AM

Porosity is one reason it's necessary

Sent from my VS920 4G using Tapatalk

Title: Re: No video/audio through Super CD-ROM² output
Post by: Raulie on June 18, 2015, 05:49:13 AM

Yes, I cleaned it first with isopropyl alcohol and cotton swabs, but it didn't work for me.